Carpet tiles having a fibrous face or wear surface and a solid backing layer composed of a hot melt composition, such as bitumen or atactic polypropylene, are well known and such carpet tiles and methods of producing such carpet tiles are described for example in U.S. Pat. No. 4,582,554, issued Apr. 15, 1986, as well as divisional U.S. Pat. No. 4,737,221, issued Apr. 12, 1988, which are hereby incorporated by reference in their entirety. These patents describe methods of producing carpet tiles with a hot melt bitumen composition backing layer by supporting a carrier, such as an endless belt or a secondary backing layer, applying a layer of a bitumen hot melt composition in liquid form to the carrier, laminating the back surface of a carpet material, which optionally may be precoated to the liquid hot melt composition on the carrier, cooling the carpet laminate and cutting the carpet laminate into carpet tile.
A laminate sheet material may be employed as the carrier belt rather than employing a separate, releasable, endless carrier belt, and also that the laminated material may become a direct part as a secondary backing of the carpet tile so produced. The backing sheet may be a laminate of glass and polythene film, that is, polyethylene film, with the film surface being applied directly to the carrier belt. Suitable laminate backing sheets disclosed include a laminate of glass and polyethylene film or glass-polyethylene-glass or a polyester fabric or paper-polyethylene film. In this method, it is essential that the expensive-type laminate backing sheets must be substantially resistant to the penetration therethrough of the hot melt, liquid composition. The backing sheet is useful in providing non-slip and dimensional stability characteristics to the resulting carpet tile.
In one method of producing carpet tile, a layer of a hot melt composition, such as a modified bitumen composition, is coated on an elongated, fibrous carrier sheet and the carrier sheet becomes a secondary backing sheet for the carpet tile. Normally, polypropylene or a blend of polypropylene and polyester non-woven fibers are employed as the secondary backing carrier sheet. However, the polypropylene sheet has a low melt and distortion temperature, for example at a temperature 20.degree. C. to 30.degree. C. below the application temperature of the hot melt composition, such as above temperatures of about 130.degree. C. The hot melt composition is applied to the carrier sheet material or a carrier belt at a temperature sufficient to provide for a liquid, viscous, hot melt composition of defined thickness, e.g. 20 to 60 mils, such as at a temperature of generally 140.degree. C. to 170.degree. C., for example 150.degree. C. to 160.degree. C., which leads to the distortion of the polypropylene fibrous sheet. Therefore, polypropylene, non-woven sheet material is not a satisfactory material as a secondary backing carrier sheet.
There has been used as a secondary backing sheet a synthetic fiber backing carrier sheet, for example, composed of expensive, high temperature-resistant polyester sheet material, such as a spun-bonded, polyester, non-woven material known as Bidim TH 100 from Rhone Poulenc. Such backing material is employed for its high heat resistance and high stability, the use of which tends to prevent built-up tensions in the resulting carpet tile and therefore to improve dimensional properties of the product. However, such high temperature resistant synthetic fibers, such as the polyester fibers, are quite expensive.
It is desirable therefore to provide a carpet tile and a method of producing a carpet tile which provides a carpet tile of improved dimensional stability at a low cost and without the difficulties and disadvantages associated with the prior art use of carrier sheet secondary backing sheets.